python[3]native: allow use of both native Python 2 and 3
Instead of both classes using ${PYTHON_PN} (which is set by python-dir and
python3-dir), hardcode the right values so that it is possible to inherit both
pythonnative and python3native at the same time.
If both are inherited then both native Pythons are available, but the last to be
inherited will be the one to set PYTHON.
Signed-off-by: Ross Burton <ross.burton@intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
